Scientists have measured the amount and distribution of dark matter in the Milky Way, they did this by timing millisecond pulsars. The study showed that the Earth contains no more than 1 kg of this exotic substance.
Dark matter in the Galaxy
A team of researchers from the University of Alabama has published a new study of the amount of dark matter in our galaxy and how exactly it is distributed in it. It can be considered the most accurate and comprehensive to date.
Scientists have been searching for dark matter for a long time and regularly publish new research on it. However, all of them still remain limited victories over its mystery. The thing is that scientists simultaneously don’t know what it is or where exactly to look for it. All we understand is that it is something invisible in any spectrum, capable of gravitational interaction, and at the same time it makes up 80% of all matter in the Universe.
Scientists have several theories as to what particles make up dark matter. However, in order to choose the right one, it is necessary either to perform very complex experiments or at least to understand how it is distributed in space. How much of it surrounds our Galaxy, how much is inside it in the form of clumps, and how much is scattered close to us.
Pulsar timing
Fortunately, there is a relatively uncomplicated method for this: timing millisecond pulsars. These neutron stars that are part of binary systems rotate incredibly fast and their period of emission of radio pulses and their frequency remain unchanged for many years. The only thing that can change them is movement due to gravity.
And the action of all the forces from visible objects in the Milky Way can be calculated. This means that if the signals of millisecond pulsars are affected by something unaccounted for, it is dark matter. And if we collect data on all such binary systems in the Milky Way, we can determine not only its number, but also where exactly it is located.
A team of scientists tried to apply this method back in 2021. However, at that time they encountered an unexpected obstacle. Stars that are components of binary systems along with neutron holes also emit charged particles. And some of them fall within the magnetic field of pulsars.
Neutron stars re-radiate them, but the process of trapping the particles grabs a tiny but measurable fraction of their rotational energy. Consequently, their rotation still slows down, and the effect of magnetic braking then couldn’t be calculated in 2021.
New findings
There is no problem with magnetic braking if there is no source of charged particles near the millisecond pulsar. And this is possible only in one case, when both objects in the system are rapidly rotating neutron stars.
Binary millisecond pulsars have been known for quite some time, but there are not many of them in the Milky Way. Therefore, the study was done then, the presence of dark matter was detected, but the distribution of dark matter could not be determined.
So after a few years, scientists were able to build a model of magnetic braking and learn how to calculate it. And it was immediately possible to use the remaining millisecond pulsars to estimate the gravitational influence of dark matter.
In particular, it turned out that there is quite a lot of dark matter inside the galaxy in its scattered form. More specifically, it should be no more than 1 kg within the Earth. This can reduce the number of candidates for its constituent parts quite a bit.
According to phys.org
